The present invention relates to a driving force distribution apparatus for distributing driving forces to be transmitted to right and left wheels.
The present application claims priority from Japanese Patent Application No. 2004-096185, the disclosure of which is incorporated herein by reference.
Among such driving force distribution apparatuses is one comprising a differential case, a differential unit, a hydraulic motor, and a hydraulic pump (see Japanese Patent Application Laid-Open No. 2003-130175). Here, a rotational driving force of a propeller shaft which is rotatably supported and connected to an engine side thereof is transmitted to the differential case through gears. The differential unit distributes and transmits an input driving force to the differential case to right and left axles by using a planetary gear mechanism. The hydraulic motor gives relative rotating forces to the right and left axles. The hydraulic pump drives the hydraulic motor for a rotation.
As shown in FIG. 6 (sectional view), the hydraulic pump 100 provided in the driving force distribution apparatus is of radial plunger type, including a cylinder block 101 and a cam ring 103. The cylinder block 101 retains a plurality of plungers 102 radially so as to be able to reciprocate. The cam ring 103 is arranged around a periphery of the cylinder block 101. The cylinder block 101 is formed integrally with a pump shaft 104. A gear 105 formed on the periphery of the differential case 10 transmits the driving force to a drive gear formed on the pump shaft 104 of the hydraulic pump 100 via an idle gear 106 for the rotation. Consequently, when the pump shaft 104 rotates, the cylinder block 101 rotates to reciprocate the plungers 102, thereby operating the hydraulic pump 100 for pumping.
A one-way clutch 107 is arranged between the pump shaft 104 and the drive gear 105. The one-way clutch 107 operates the hydraulic pump 100 only when the vehicle is running forward, and stops the pumping operation of the hydraulic pump 100 when the vehicle is running backward. Since the power is transmitted thereto from the propeller shaft 5 through the differential case 10, the hydraulic pump 100 is driven to rotate not only when the vehicle is running forward but also when running backward. The direction of rotation of the hydraulic pump 100 in the forward running is opposite from in the backward running. This reverses a suction oil channel and a discharge oil channel connected to the hydraulic pump 100 in usage. Since the hydraulic oil is sucked through the discharge oil channel which is designed for higher pressures and has a smaller cross section, a cavitation can occur at the side of the suction oil channel which has a larger cross section. Oil leakage can also occur. The one-way clutch 107 mentioned above is thus provided in order that the hydraulic pump 100 shall make its pumping operation only in the forward running.
As above, the hydraulic pump provided in the conventional driving force distribution apparatus for right and left axles is stopped when the vehicle runs backward. During the backward running, what are transmitted to the right and left wheels are evenly distributed driving forces alone. It is therefore impossible to apply relative rotating forces to the right and left axles.
Then, the one-way clutch may be eliminated while cross sectional area is increased in the oil channel leading to the suction side of the hydraulic pump rotating in the reverse direction when the vehicle runs backward. This can produce the problem, however, that the driving force distribution apparatus for right and left the axles is increased in complexity and in size, making it difficult to mount the driving force distribution apparatus on the vehicle.